we bought a big fresnel lens at exclusive, we cut it half, did we do right?

You don't cut a lens in half, rather you need to buy two lenses. A fresnel lens has a "center" and that center must be aligned along the centerline of the projector.

You don't cut a lens in half, rather you need to buy two lenses. A fresnel lens has a "center" and that center must be aligned along the centerline of the projector.

I've seen ppl cut it ? . can I cut it but still keeping the center?

does this means, that I cant turn one fresnel into two ? I must buy two fresnels

we bought this fresnel

http://www.exclusiv-online.com/shop/index....t&art=FD210

says it's divisible into two single fresnel lenses. what do they mean?

think we cut it wrong lol, shouldnt cut it half .... should just divided the thickness


any recommendation where I can get new fresnels ? and fast?

Yes that fresnel was supposed to be split apart. It's two fresnels glued together.

Where are you located ?

In the US you can get fresnels from right here at LL.

In the UK area go to www.3dlens.com

I'm Sweden europe..

3dlens got fast shipping in europe?

will this http://www.3dlens.com/shop/large-fresnel-lens-a260.php be a good replacer for the old one?

3dlens is fast enough to the US but I don't know about europe?

The 200mm would work for your rear fresnel. You would need to make sure the lamp is around 190mm from the rear fresnel.

Your front fresnel needs to match the triplet. What is the focal length of the triplet?

Reflector + 1mm to HQI + 23.85mm to condensor + 136.15mm to fresnel + 285 to 330mm to objective

something like that..

Well the 200mm should work but you may have to move the Lcd a bit and maybe adjust the condenser a bit.

And you need a 330mm fresnel for the front lens.

http://www.3dlens.com/shop/large-fresnel-lens-a395a.php

the focal length?

Putting it Together

Look at this illustration:



Number 1 is our point light source, the 65K T15 lamp. It is important that the lamp center (arc) be on center (line X) with the entire enclosure and at the focus of the first fresnel (3a). The fresnel lenses (3a+ and projection lens (5) can be purchased from the Lumenlab store. The Lumenlab S15 fresnels have been specially made for a 15" projector. They are already the proper size, groove pitch and thickness. The fresnel lens on the lamp side has a shorter focal length of ~220mm, and the fresnel lens facing the projection lens has a focal length of ~317mm. This is advantageous because we can have the lamp a little closer to the lens, which means less light is ‘lost’. Our piece of isolation glass (2) makes a great mount for the collimator fresnel. Never mount the fresnel on the lamp side of the glass, it will melt! The isolation glass (2) should be a piece of 1/8” tempered glass cut to size. Lexan can also be used. These are readily available at most hardware stores for a few dollars, but tempered glass can take a week to obtain so plan ahead.

Be sure to tell the hardware store that you do NOT want your tempered glass to have a stamp or bug (safety glass label). If they stamp it the stamp might be in the way of the projection.

Size the isolation glass 1/2” shorter than your enclosure height. This is so that the glass can sit off of the bottom by 1/2” which is necessary for #Keeping it Cool (explained later).

The S15 projection lens (5) is a 320mm focal length lens triplet. It is important that the projection lens be centered to the other lenses and the enclosure (line *X*).



So we know that 1 is our lamp, 2 is our isolation glass, 3a+b are the (a) collimator and ( collector fresnel lenses, 4 is our lcd panel and 5 is our projection lens. The collimator fresnel has a rear focal length of 220mm, so we would position the center of the lamp 220mm away, as represented by line X. The collector fresnel has a forward focal length of 330mm, but we would position our projection lens ~320mm *away from the collector* as represented by line Y. The reason for this is because we want to use the entire projection lens’ area, not just the center. The illustration shows that the projection lens is positioned slightly before the focus of the forward fresnel lens.

Our projection lens may have a focal length of 320mm, but the if the lens were only placed at its focal length from the LCD panel we would be focused on infinity, so in practical usage we would place it around ~340mm from the LCD panel as represented by line Z (note this distance will vary with different screen sizes). We leave a gap of ~15mm between the condenser fresnel lens and the LCD panel and a gap of ~20mm between the collector fresnel and the LCD panel. This is desirable because if a fresnel lens is too close to the panel, the grooves on the fresnel lens will be projected too. The larger gap for the collector fresnel is to give some room for keystone tilting if needed. If you have circular lines or Moire patterns in your projection your fresnels are too close to the panel.

If you are making a focusing mechanism for your lens, you’ll want about 50mm (~2”) of movement in the projection lens which would accommodate virtually every usable setting in which you would use your projector. This means your projection lens range would be 320mm to 370mm from the LCD panel.

I'm Sweden europe..

3dlens got fast shipping in europe?

Sure you can cut it! What Durachko meant was simply that you need to cut in a way so that the center of the lens remains in the center!

This means that you'll have to cut equal parts of the lens' both sides. By doing this the center remains in the center of the fresnels. Doing otherwise might create some rather characteristic results